In wireless communication systems, wireless service providers may operate radio access networks (RANs), each RAN including a number of base stations radiating to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a RAN may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WiFi), BLUETOOTH, and others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
In accordance with the air interface protocol, each base station may provide wireless service to UEs on one or more carrier frequencies, or “carriers”, each of which could be frequency division duplex (FDD), defining separate frequency channels for downlink and uplink communication, or time division duplex (TDD), defining a frequency channel multiplexed over time between downlink and uplink use. Each carrier or its respective channels could be within a defined frequency band and could be of a particular frequency bandwidth, such as 5 MHz, 10 MHz, or 20 MHz for instance. A given base station could be arranged to serve a UE on a single such carrier at a time or, with carrier aggregation service or the like, on multiple carriers at a time.
Each carrier may also define various logical channels to facilitate communication between the base station and one or more served UEs. For instance, on the downlink, a carrier may define a reference channel on which the base station broadcasts a reference signal useable by UEs to detect and evaluate coverage, various other downlink control channels to carry control signaling (such as resource-scheduling directives) to UEs, and one or more shared or traffic channels for carrying bearer data (e.g., user or application level data) to UEs. And on the uplink, a carrier may define one or more uplink control channels to carry control signaling (such as resource scheduling requests) from UEs, and one or more shared or traffic channels for carrying bearer data from UEs. In practice, the shared or traffic channels may define particular physical resources for carrying data between the base station and UEs.
When a UE initially enters into coverage of a RAN (e.g., powers on or moves into coverage of the RAN), the UE may detect a reference signal and read system information broadcast from a base station of the RAN and may engage in a process to register itself with the base station and generally by the RAN. For instance, the UE may transmit an attach or registration message on an uplink control channel to the base station, and the base station and/or supporting infrastructure may then responsively authenticate and authorize the UE for service, establish a record indicating where in the RAN the UE is operating, establish local profile or context records for the UE, and provide an attach accept or registration response message to the UE. Thereafter, the UE may then be served by the RAN in an idle mode or a connected/active mode.